Why is there a knocking noise when we turn the steering wheel? It doesn't do it if we just turn it a little, but when making a full turn, there is a rather loud knocking/clicking noise.

Do you feel it in the steering wheel? if so it could be the intermediate steering shaft. If not it could be a sway bar link or bushing.

Sounds like CV joints(Front-wheel drive) need to be inspected / replaced..

Check your power steering fluid. Screeching will come from the fluid being too low and would affect the steering. It will also burn out the pump if you don't keep it full.

First I was going to say the valves were damaged from the heat or lack of oil, but that would not make sense if the steering wheel is turned.
The power steering is about the only thing affected by the steering wheel.
I would take a piece of heater hose and use it as a stethoscope to listen around the pulleys for the noise with someone turning the wheel.

Have you checked the power steering fluid level? The reservoir for the fluid will be at the front of the engine, where the belt runs the power steering pump. If it's low or out add a little power steering fluid till full, then start car and slowly turn wheels back and forth from stop to stop-not too ******* the stops (when the steering won't turn further that way...that's what I mean by stops)....Turn wheel one way full travel, then reverse and turn the other way. Check the fluid level again, and add as needed.
If fluid is not low, the belt may be too loose to make the power steering pump work, or you may have a bigger problem that needs professional attewntion.

if the noise happens when the car is moving then you're hitting theh wheel stop that prevent the wheel from rotating around. typically the wheel stop looks like the back of a cupped hand and its located on the lower control arm that comes off the strut. smear some grease on it and that will probably eliminate the noise.

on some cars the noise is from the strut bearing on top. the strut bearing is located on the top of the strut tower. You can hear that noise if you stand on the side of the car with the hood open and then have someone turn the wheel until the noise comes in. the car doesn't need to be moving to hear a bad strut bearing.

lastly, check the belt tension for the power steering belt as the belt may be slipping under the load of a full turn

Check the fluid level and note where it is.Also,do you think the fluid looks clean?
Staying clear of the drive belt, wrap a rag tightly around the top of the fluid reservoir. Make sure it can't get into the drive belt or any pulleys.
Now start the car and turn the steering wheel left and hold it on the stop(you'll hear a noise which means the fluid is bypassing).After holding it at full left for 5 seconds(count them off), turn the steering to the full right position and hold it for the full 5 count.This helps remove any air in the system.
After a minute you can repeat this. Now stop the engine and check the reservoir.Did the level change? If so,that much air was removed.
Did it overflow onto the rag? You can repeat this if it helps.If it doesn't,you have bigger problems.(:^) don-ohio

most cars have a steering lock that engages when you turn off the car. If you try wiggling the wheel while you turn the key, that might free up your steering. If just wiggling it a little does not work, try pulling it one way and turning the key, giving it a little force turning the wheel (sometimes the wheel locking mechanism gets stuck) ... if it still doesn't work, try turning the wheel the other way and turning the key. If you are still locked up .. you'll probably need to see a mechanic about it. Hopefully the wheel lock is just a little stuck and you can free it up yourself -- it's free that way :-)

there is a problem with the steering shaft going to gear box 2 out of 10 trucks have this problem gmc and chevy ive done a few, its a dealer part, replace that first then see if the other rubbing noise is there, but the knock noise is the shaft, i had 2 with about that mileage they were out of warranty, good luck start there first.

Hi these cars are known for the wishbone bushes failing and will cause the same symptoms as what you describe, there are 3 different bushes on the wishbone have them all checked for any play, Hope this helps